By Daniel Roytas MHSc (Nut), BHSc (Nat), Dip. RM, MANTA
Could it be possible that widespread, subclinical vitamin A deficiency exists in the Australian population? According to the Australian Department of Health, vitamin A deficiency is thought to be rare1. However, the 2011-2012 Australian Health Survey found that 33% of males and 27% of females aged 14 - 18 years, and approximately 20% of individuals aged 19 – 50 years had inadequate intakes of vitamin A2. Note that the RDI for vitamin A is 900 µg/day for men and 700 µg/day for women3.
There are a number of recent case studies in the peer reviewed literature that have found severe ocular diseases in Australian children4 and adults5 arising from inadequate dietary vitamin A intake. A 2016 study published in the Journal of Paediatrics and Child Health found that 36.5% of children presenting to the Sydney Children’s Hospital with ocular disease had vitamin A deficiency6. Many of these cases are irreversible (blindness) and could have been completely prevented with adequate vitamin A intake. This data highlights the fact that vitamin A deficiency is present amongst the Australian population, however the true prevalence is yet to be determined.
According to the Australian Government, vitamin A deficiency is rare because of the relatively high amounts of beta-carotene (provitamin A) that is present in vegetables2. Yet, in countries with endemic deficiency, the main dietary source of vitamin A is from plant derived carotenoids such as beta-carotene7. This might suggest that animal sources of vitamin A are required to prevent widespread deficiencies amongst the population.
A medium sized sweet potato provides 438% of the RDI for an adult male, a medium sized carrot provides 204% of the RDI8 and 100g of spinach provides 188% of the RDI9. Surely the population would be eating enough vegetables to meet their vitamin A requirements? A 2018 report released by the Australian Bureau of Statistics found that just 7.5% of the entire population are eating the recommended intake of vegetables10. Sufficient intake of beta-carotene can prevent vitamin A deficiency, however the Australian population may just not be eating enough of it.
Beta-carotene must be converted to vitamin A by enterocytes within the small intestine11. This process seems to be fairly inefficient and consequently the bioavailability of beta-carotene ranges from 5 – 65%12, which is considerably less than the 75 – 100% bioavailability provided by animal sources13. Therefore, conditions affecting gut function such as gastro-esophageal reflux disease (GORD)6 and short bowel syndrome14 may impair the absorption of beta-carotene to an even greater extent. Furthermore, chemical pesticides used in the cultivation of vegetables have been shown to reduce beta-carotene to undetectable levels15 and the retention of beta-carotene in many vegetables is also reduced by cooking16. The consumption of organic vegetables would somewhat contribute to overcoming this issue as they have been shown to have higher concentrations of beta-carotene than non-organic vegetables17. However, according to the 2018 Australian Organic Market Report, just 12% of Australians purchase organic vegetables on a regular basis18.
Preformed vitamin A is found in animal products such as organ meats, milk and eggs. The highest vitamin A containing food is liver, with 100 g providing 1500% of the RDI8 however less than 1.0 g of organ meat is consumed by the average Australian on a daily basis19. It’s no wonder that in pack animals like wolves, the leader of the pack eats the liver of its prey before any of the other animals are allowed to eat. Cod liver oil is also another good source of vitamin A, with 1 teaspoon (5mL) containing 250 µg or 27% of the RDI for an adult male20. The Australian Bureau of Statistics states that milk products are the second largest contributor to vitamin A intake (after vegetables)2. Interestingly, one serve (244 mL) of cow’s milk provides just 7.6% of the RDI, which means that an adult male would need to consume approximately three liters of milk per day to meet their vitamin A requirement21. Whilst eggs also contain vitamin A, an adult male would need to consume seven of them every day just to meet their requirements8. Obviously the amounts of these foods required to meet the RDI would be considerably lower with a diet that includes a range of vitamin A containing foods. Interestingly, this vitamin seems to be one of the most negatively affected nutrients in individuals with disordered eating22.
Vitamin A deficiency is quite concerning for a number of reasons. Firstly, mild deficiencies are often not associated with any symptoms23, whereas more severe deficiencies are associated with a sudden onset and rapid progression of potentially irreversible ocular diseases24. Unfortunately severe deficiencies are often not identified until it is too late (irreversible blindness)4. Therefore clinicians should be aware of the early warning signs of vitamin A deficiency including frequent infection due to impaired immune function25, keratosis pilaris (small red raised bumps that frequently present on the backs of the arms)26, delayed wound healing27, dry eyes28 and deteriorating vision at night29. Secondly, vitamin A deficiency is associated with significant maladies of the gastro-intestinal system. For example, vitamin A deficiency is associated with intestinal barrier dysfunction30 and increased gut permeability in humans31. In rats, vitamin A deficiency has been shown to cause atrophy of the microvilli, a reduced number of goblet cells and enterocytes32, lower levels of brush border enzymes32,33 and increased bacterial translocation (sepsis)33. Whilst human trials in this area are lacking, could it be possible that vitamin A deficiency disrupts intestinal function to such an extent that malabsorption of many other vitamins and minerals occurs? Is this one of the reasons we are seeing such drastic increases in chronic disease in recent times?
Given this information, it makes sense why our mothers and grandmothers forced us to take a teaspoon of cod liver oil every day and meals like liver and bacon were frequently served at the dinner table. Unfortunately, these dietary habits have fallen by the way side in recent times. In a 2008 paper34, the Editor in Chief of the Medscape Journal of Medicine, Professor George Griffing said “It is wise to remember to listen to your mother – at least about cod liver oil”. Our ancestors really were on to something. They knew that we had to eat vitamin A rich foods like organ meat and cod liver oil to achieve an optimal vitamin A status to maintain good health. It would seem that the time has come to make consuming such foods fashionable again, for the health and wellbeing of all Australians.
Note: This article is for general information purposes only. It does not constitute as health advice and does not take the place of consulting with your primary health care practitioner.
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